The present invention relates generally to operations performed and equipment utilized in conjunction with a subterranean well and, in particular, to safety valves having redundant operators or systems.
Subsurface safety valves are well known in the oil and gas industry and act as failsafes to prevent the uncontrolled release of reservoir fluids in the event of a worst-case-scenario disaster. Typical subsurface safety valves are flapper-type valves that are opened and closed with the help of a flow tube moving telescopically within the associated production tubular. The flow tube is often controlled hydraulically from the surface and is forced into its open position using a piston and rod assembly that may be hydraulically charged via a control line linked to a hydraulic manifold or control panel at the well surface. When sufficient hydraulic pressure is conveyed to the subsurface safety valve via the control line, the piston and rod assembly forces the flow tube downward, which causes the flapper to move downward to the open position. When the hydraulic pressure is removed from the control line, the flapper can move into its closed position.
Some safety valves are arranged thousands of feet underground and are therefore required to traverse thousands of feet of production tubulars, including any turns and/or twists formed therein. Consequently, during its descent downhole, the control line for an associated safety valve may undergo a substantial amount of vibration or otherwise sustain significant damage thereto. In extreme cases, the control line may be severed or one of the connection points for the control line may become inadvertently detached and/or damaged either at a surface well head or at the safety valve itself, thereby rendering the safety valve potentially powerless and inoperable. Moreover, during prolonged operation in downhole environments that exhibit extreme pressures and/or temperatures, the hydraulic actuating mechanisms used to move the flow tube may fail due to mechanical failures such as seal wear and the like. As a result, some safety valves prematurely fail, thereby leading to a need for redundant safety valve operators or systems.